The present invention relates to a plate mounting apparatus for a printing press, which winds, on the circumferential surface of a plate cylinder, a plate having one end gripped by a leading-side plate lockup device provided in the gap formed in the outer circumferential surface of the plate cylinder, and causes a trailing-side plate lockup device in the gap in the outer circumferential surface of the plate cylinder to grip the other end of the plate, thereby mounting the plate on the plate cylinder.
In a general printing press, leading- and trailing-side plate lockup devices each including a plate lockup table and gripper plates pivotally supported by the plate lockup table are provided in a gap formed in the outer circumferential surface of a plate cylinder. The leading end of a plate is gripped by the leading-side plate lockup device by the opening and closing operations of the gripper plates, and wound on the circumferential surface of the plate cylinder by rotating the plate cylinder by almost one revolution, and thereafter the gripper plates are opened and closed so that the trailing-side plate lockup device grips the trailing end of the plate, thereby mounting the plate on the plate cylinder.
In a printing operation, an ink and water are supplied to the surface of the mounted plate to form an image, and the image is transferred to paper being transported directly or through a blanket cylinder, thereby printing the image.
In this printing operation, when the plate is distortedly mounted, the image is distortedly printed, degrading the quality of the printed matter. Especially, in multicolor printing, the different colors are misregistered to largely degrade the quality of the printed matter.
In order to resolve this problem, conventionally, pin holes are formed at the predetermined positions of the plate, or substantially cross-shaped register marks are drawn at the predetermined positions of the plate before a pattern is printed on the plate for plate making. The position of the pattern is determined with reference to these pin holes or register marks or the like, thereby performing print making. Then, with reference to the above-described pin holes, register marks, or the leading end of the plate, U-shaped reference pin holes open at the leading end of the plate are formed at the leading end portion of the plate by a known plate punching machine. Thereafter, the plate is mounted on the plate cylinder while engaging the reference pin holes formed in the plate with the reference pins provided on the plate gripper portion of the leading-side plate lockup device.
More specifically, when the plate lockup device is caused to grip the plate during plate mounting operation, the gripper plates of the leading-side plate lockup device are opened, and the leading-side end portion of the plate is inserted into the gripper portion between the gripper plates and the plate lockup table while engaging the reference pins of the plate with the reference pin holes of the plate lockup device. After the U-shaped bottom portion of the reference pin hole is brought into contact with the reference pin to position the plate, the gripper plates are closed, and the end portion of the plate is gripped by the plate lockup device.
In such a conventional plate mounting apparatus, however, the operator visually checks whether the U-shaped bottom portion of the reference pin hole contacts the reference pin. Although a skilled operator is required, variations caused by the degrees of skills of the operators are inevitable so that satisfactory positioning precision cannot always be obtained. Accordingly, work with a cramped posture in a narrow space overloads the operator.